The present invention relates to a process for mixing a polytetrafluoroethylene molding powder and an organic filler.
The molding powder of polytetrafluoroethylene (hereinafter referred to as "PTFE") is a PTFE powder prepared by finely dividing coarse particles obtained by suspension polymerization, and it has been used for molding by means of compression molding or ram extrusion. The particle size of the finely divided PTFE particles (primary particle size) is 5 .mu.m at the smallest and is up to about 1,000 .mu.m. Usually, the particle size is not more than 100 .mu.m. The PTFE molding powder into which glass beads or powder, glass fiber, carbon, graphite, molybdenum disulfide, bronze powder, or various kinds of heat resistant synthetic resins such as polyimide, polyamideimide and polyphenylene oxide, are incorporated as a filler in order to improve the abrasion resistance, hardness or the like, has also been used as a filled PTFE molding powder. The mixing of the powder and filler can be practiced by a dry mixing method or a wet mixing method.
The PTFE molding powder must be mixed uniformly with the filler, but a difficulty has been encountered in mixing the PTFE powder with organic fillers uniformly by a dry method because the organic filler charges with electricity and sticks to the wall of a mixing machine. The dry method also has the disadvantage that the filler is apt to come off or separate from the mixture and the moldings prepared therefrom may have poor appearance or decreased mechanical strength.
The primary object of the present invention is to provide a process for mixing PTEF molding powder with organic fillers, which can eliminate the above-mentioned problems of conventional process.
The above and other objects of the present invention will become apparent from the description hereinafter.